Polybutylene terephthalate resin is used in a wide range of fields as an engineering plastic, such as automobile parts, electric/electronic parts due to the excellent mechanical properties, electric properties, and other physical and chemical properties, along with good workability. In particular, in order to protect the contents from damages caused by moisture, dust, external shock, and the like, polybutylene terephthalate resin is preferably used for the casing containing substrate mounted with electronics parts thereon, and the insert-molded products on which sensor probe, connector terminal, and the like are mounted, and the like.
In these applications, for the purpose of avoiding as much as possible, the influence of moisture, dust, and the like on the substrate and the sensor body, a potting material is often heat cured by being filled in a cover with a substrate stored therein or a cover and a casing are often bonded and sealed with an adhesive. As such potting material and the like, epoxy resin and silicone rubber are often used, and specifically silicone rubber is often used for the parts requiring heat resistance and cold resistance. Recently, various joining methods such as double molding, hot-plate welding, vibration welding, and laser welding have been put into practical use. As for the potting intended for protecting the substrate, silicone rubber is widely used independent of the joining methods.
Furthermore, silicone rubber is also used in a method of simple joining of the circuit parts of capacitor and the like, and specifically an addition-reaction type silicone rubber is often used to shorten the curing time. The term “silicone rubber” referred to herein signifies a liquid silicone rubber used as an adhesive and for potting electric/electronic parts. The silicone rubber is largely divided into two types: addition-reaction type silicone rubber; and condensation-reaction type silicone rubber.
In the application where the above methods are used, there are normally arranged metal terminals such as connector, metallic bus bar constituting electric circuit, varieties of sensor parts, and the like by pressure-working or insert-molding. Specifically in applications for parts mounted on automobile, high durability is required in many cases in an environment of high temperature/high humidity and of heating and cooling cycles. Accordingly, there are commonly used polybutylene terephthalate materials characterized by elastomers and various additives.
Depending on the selection of the material of casing and cover, however, there were cases where that kind of silicone rubber caused poor curing and poor adhesion at the interface, and thus was unable to exert sufficient function as the parts, in some cases.
JP-A 9-165503 proposes a composition containing polybutylene terephthalate, a specified silicon compound, a phenol-based antioxidant and/or a thioether-based antioxidant in order to improve the adhesion strength to an addition-reaction type silicone.
That kind of composition, however, cannot satisfy the heating and cooling cycle resistance of the material required in the automobile industry. Generally it is known that the addition of a specific silicon compound in large amounts deteriorates the physical properties of silicone rubber, and the presence of sulfur-based compound and trivalent phosphorus compound deactivates the platinum compound in the curing catalyst to thereby inhibit the reaction. Therefore, the composition disclosed in JP-A 9-165503 is not practically applicable.
JP-A 2006-111693 describes the improvement of heat shock resistance of an insert-molded product in terms of the composition composed of polybutylene terephthalate along with additives of an isoprene-butadiene-styrene-based copolymer, a polycarbonate and/or a vinyl-based copolymer. The disclosure, however, does not contain the description about the adhesion to silicone rubber. Furthermore, the addition of vinyl-based copolymer and polycarbonate may lower the adhesion to silicone rubber.
JP-A 6-32912 describes that a composition of polybutylene terephthalate to which SEBS is added by a vent-type injection molding machine without applying a melt-kneading process provides good mechanical strength, heat resistance, impact resistance, and chemical resistance. For the adhesion to silicone rubber, however, no description is given therein.
JP-A 10-235819 describes that the epoxy-adhesion improves by blending a polyester with a block polymer composed of a polymer block containing mainly a vinyl aromatic compound and a polymer block containing mainly a non-hydrogenate and/or a hydrogenated conjugate diene compound. The disclosure, however, does not describe about the adhesion to silicone rubber. Furthermore, it was confirmed that a non-hydrogenated conjugate diene compound lowers the adhesion to an addition-reaction type silicone rubber.